Coating device and coating method

ABSTRACT

A coating device has: a die head that is provided with a supply port into which a coating slurry is supplied, a manifold that stores the coating slurry, and a slit that dispenses the coating slurry; a supply pipe that is connected to the supply port of the die head; and a cover plate that is provided in the supply port or the supply pipe and that reduces the flow rate of the coating slurry at the center of a cross-section that is orthogonal to the direction in which the coating slurry in the supply port or the supply pipe flows into the die head.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.15/756,710, filed Mar. 1, 2018, which is a National Stage ofInternational No. PCT/JP2016/076160 filed Sep. 6, 2016 claims priorityto Japanese Patent Application No. 2015-185492, filed Sep. 18, 2015.

TECHNICAL FIELD

The present invention relates to a coating device and a coating methodfor forming a coating active material layer on a current collector.

BACKGROUND ART

A laminated type cell is known as an example of a secondary battery. Alaminated type cell has a construction in which positive-electrodesheets and negative-electrode sheets that are alternately and repeatedlystacked on each other with separators interposed therebetween. Each ofthe positive-electrode sheets and the negative-electrode sheets isconfigured an active material layer coated uniformly on a currentcollector. An example of a coating device for fabricating electrodesheets is disclosed in Patent Document 1.

An example of a relevant coating device and coating method are nextdescribed.

FIG. 8 and FIG. 9 are drawings showing an example of the configurationof a related coating device. FIG. 8 is a side view of the relatedcoating device, and FIG. 9 is a top view of the principal parts of thedevice. In FIG. 8, moreover, a portion is shown in a transparent viewfor the purpose of explanation.

As shown in FIG. 8, the coating device includes: roller 210 whichrotates in synchronization with the take-up speed of current collector200 and through which current collector 200 is transported when currentcollector 200 that has been set in a pay-out portion (not shown in thefigures) is being taken up toward a take-up portion (not shown in thefigures); and die head 230 that dispenses coating slurry 220 thatcontains an active material upon current collector 200. Die head 230 hasmanifold 231 that stores coating slurry 220 that is supplied and slit232 that dispenses coating slurry 220 that is stored in manifold 231 tocurrent collector 200. Coating slurry 220 is supplied from a pump (notshown in the figures) to die head 230 by way of gate valve 250 andsupply pipe 240.

Coating slurry 220 that is stored in manifold 231 is extruded to currentcollector 200 through slit 232 under the pressure of coating slurry 220that is supplied from the pump (not shown). Coating active materiallayer 222 realized by coating slurry 220 is uniformly formed on currentcollector 200 by the take-up of current collector 200 toward the take-upportion (not shown) together with the rotation of roller 210.

As shown in FIG. 9, coating slurry 220 that flows into manifold 231 byway of supply pipe 240 is dispensed onto current collector 200 by way ofslit 232 and coating active material layer 222 is formed on currentcollector 200. In the following explanation, the direction in whichcoating slurry 220 is dispensed from slit 232 is referred to as thecoating direction. In addition, the direction perpendicular to thecoating direction is referred to as the width direction of currentcollector 200, manifold 231, slit 232, and coating active material layer222. In FIG. 9, the coating direction and width direction are indicatedby arrows.

When an aqueous slurry is used as the coating slurry in the process ofcoating a negative-electrode, the problem arises that there are localsites, in which the coating weight of active material per unit areaincreases, in the width direction of the current collector.

FIG. 10 is a graph showing the coating weight of active material perunit area in the related coating method. The coating weight of activematerial per unit area was measured at 19 measurement points in thewidth direction of the current collector and the average value is takenas 100%. The horizontal axis of the graph shown in FIG. 10 shows thepositions of the measurement points of the coating active materiallayer. The vertical axis of the graph shows in percentage the shiftbetween the average value and the measured value at each measurementpoint.

Referring to FIG. 10, there clearly are sites at which the coatingweight of active material per unit area is markedly greater than theaverage value, and further, sites at which the coating weight of activematerial per unit area is markedly smaller than the average value. Thedifference between the maximum value and minimum value of the coatingweight of active material per unit area is approximately 3% of theaverage value of the coating weight of active material per unit area.The variation (standard deviation) is 0.70%.

An example of a method of making the thickness of the coating activematerial layer uniform is disclosed in Patent Document 2.

In the method disclosed in Patent Document 2, a flow adjustment plate isprovided in a pocket that corresponds to the manifold of the die head.The flow adjustment plate is provided with a plurality of through-holeshaving differing aperture areas. The aperture area of through-holes isat a minimum in the vicinity of the coating material supply port of thepocket and the aperture area of through-holes gradually increases withincreasing distance from the coating material supply port.

PRIOR ART DOCUMENTS Patent Documents

Patent Document 1: Japanese Patent Application Laid-open No. 2012-61444

Patent Document 2: Japanese Patent Application Laid-open No. 2000-708017

SUMMARY OF THE INVENTION Problem to be Solved by the Invention

In the method disclosed in Patent Document 2, the flow adjustment platemust be produced to fit the shape of the pocket of the die head, and theflow adjustment plate must be inserted into the pocket with no gaps.

The present invention was realized to solve the problems inherent in theabove-described technology and an object of the present invention is toprovide a coating device and coating method that more readily enable animprovement in the uniformity of the thickness of a coating activematerial layer.

Means for Solving the Problem

The coating device of the present invention for achieving theabove-described object is of a configuration that includes:

a die head that is provided with a supply port into which coating slurryis supplied, a manifold that stores the coating slurry, and a slit thatdispenses the coating slurry;

a supply pipe that is connected to the supply port of the die head; and

a cover plate that is provided in the supply port or the supply pipe andthat reduces the flow rate of the coating slurry in the center of thecross-section that is orthogonal to the direction in which the coatingslurry flows into the die head, in the supply port or the supply pipe.

In addition, the coating method of the present invention is a coatingmethod that uses a coating device that is provided with at least a diehead provided with a supply port into which coating slurry is supplied,a manifold that stores the coating slurry, and a slit that dispensescoating slurry that is stored in the manifold and a supply pipe havingone end connected to the supply port and the other end connected to agate valve that switches between supplying and cutting off coatingslurry; the method including steps of reducing the flow rate of thecoating slurry in at least the central portion of a cross-section thatis orthogonal to the direction of advance of coating slurry in thesupply pipe and supplying the coating slurry to the supply port.

Effect of the Invention

According to the present invention, thickness uniformity of a coatingactive material layer can be easily improved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an image showing the differences of the flow rate of coatingslurry in a supply pipe.

FIG. 2 shows the principal parts of the configuration of the coatingdevice of the present exemplary embodiment.

FIG. 3 is a top view showing an example of the configuration of thecover plate shown in FIG. 2.

FIG. 4 is a transparent view when the die head shown in FIG. 2 is viewedfrom above.

FIG. 5A is a top view showing the configuration of Modification 1 of thecover plate shown in FIG. 2.

FIG. 5B is a side view of the cover plate of Modification 1 shown inFIG. 5A.

FIG. 6 is a graph showing the measurement results of the coating weightof active material per unit area when using the cover plate ofModification 1.

FIG. 7A is a top view showing the configuration of Modification 2 of thecover plate shown in FIG. 2.

FIG. 7B is a top view showing the configuration of Modification 3 of thecover plate shown in FIG. 2.

FIG. 7C is a top view showing the configuration of Modification 4 of thecover plate shown in FIG. 2.

FIG. 8 shows an example of the configuration of a related coatingdevice.

FIG. 9 shows the die head shown in FIG. 8 when viewed from above.

FIG. 10 is a graph showing the measurement results regarding the coatingweight of active material per unit area realized by a related coatingmethod.

EXEMPLARY EMBODIMENT OF THE INVENTION

When an NMP (N-methyl-2-pyrrolidone) slurry is used as the coatingslurry to overcome the above-described problem, the occurrence oflocalized increases in the coating weight of active material per unitarea as shown in FIG. 10 virtually ceases. The inventors focusedattention on the flow rate of the slurry in the supply pipe. If theslurry is assumed to be a laminar flow, the flow of slurry within around pipe becomes a Hagen-Poiseuille flow.

FIG. 1 is an image showing the differences in flow rate of slurry in asupply pipe. FIG. 1 is a cross-section view in which supply pipe 102 iscut parallel to the direction of flow of the slurry. The lengths of thearrows shown in FIG. 1 represent the magnitudes of the flow rate ofslurry 101. As shown in FIG. 1, the flow rate of slurry 101 is greaterin the vicinity of the center in supply pipe 102 and decreases withproximity to the wall surfaces.

Because the surface tension of water is approximately 1.8 times thesurface tension of NMP, an aqueous slurry tends to result in moredifferences in flow rate than an NMP slurry.

The inventors believe that turbulent flow occurs in the manifold when anaqueous slurry is supplied to the die head while flow rate differencesare maintained without change in the supply pipe, and that localizedincreases in the coating weight of active material per unit area of thecoating active material layer occur as a result. The inventors arrivedat the concept of the coating device and coating method by inferring thecause of the occurrence of this problem.

Exemplary embodiments of the coating device and coating method of thepresent invention are next described.

The configuration of the coating device of the present exemplaryembodiment is first described.

FIG. 2 shows the principal parts of the configuration of the coatingdevice of the present exemplary embodiment.

The coating device has: die head 10 that dispenses coating slurry 50that is supplied from the outside, onto a current collector (not shown),and cover plate 20 that reduces the differences in flow rate of coatingslurry 50 in supply port 13 of coating slurry 50 to die head 10.

Die head 10 is provided with supply port 13 of coating slurry 50,manifold 12 that stores coating slurry 50, and slit 11 that dispensescoating slurry 50. Aperture 14 for supplying coating slurry 50 fromsupply port 13 to manifold 12 is formed in die head 10. Coating slurry50 that is supplied to die head 10 passes through supply port 13 and isstored inside manifold 12, and this stored coating slurry 50 is thendispensed by way of slit 11 to a current collector (not shown).

In FIG. 2, cover plate 20 that is provided in supply pipe 30 is shown tobe bonded to die head 10, but cover plate 20 may be arranged in supplypipe 30 between supply port 13 of coating slurry 50 of die head 10 andgate valve 40. Gate valve 40 switches between supplying and cutting offcoating slurry 50. By positioning cover plate 20 in the vicinity of thedie head, coating slurry 50 that passes by way of cover plate 20 issupplied to die head 10 in a stable state and good coating conditionsare realized despite changes in the flow rate caused by pulsation of thepump (not shown) for supplying coating slurry 50 or by opening andclosing of gate valve 40.

In addition, supply pipe 30 further includes a junction part (notshown), and cover plate 20 is preferably incorporated in this junctionpart such that regardless of the shape of cover plates 20, they can beinterchanged depending on coating slurry 50. The junction part is, forexample, a joint that connects two supply pipes. If the junction part isof a type in which two flange joints are secured by a clamp, the worker,after unfastening the clamps and exchanging cover plates 20 between thetwo flange joints, only needs to engage the clamp and secure the twoflange joints. In this case, the work required to exchange cover plates20 is made easier.

By providing cover plate 20 immediately before die head 10 as describedhereinabove, when coating slurry 50 flows into manifold 12, stablecoating can be realized without any turbulence occurring inside manifold12. In particular, the effect of a superior stabilized coating isobtained in the case of a construction in which coating slurry 50 fromsupply port 13 flows into manifold 12 by way of aperture 14 that isdisposed at least in the vicinity of the center in the width directionof manifold 12.

Explanation is next presented below regarding a case in which coverplate 20 is provided in supply pipe 30 that is connected to supply port13 of die head 10 as shown in FIG. 2, but cover plate 20 may also beprovided inside aperture 14 between manifold 12 and supply pipe 30. Inaddition, supply pipe 30 is a round pipe in the present exemplaryembodiment.

The configuration of cover plate 20 shown in FIG. 2 is next described.

FIG. 3 is a top view showing an example of the configuration of thecover plate. Here, in the interest of simplifying the explanation, theX-axis and Y-axis are defined as shown in FIG. 3.

As shown in FIG. 3, the cover plate has frame-shaped edge portion 23along the walls of supply pipe 30 shown in FIG. 2 and convex-shapedrestraining plates 22 a and 22 b that extend in the direction toward thecenter of the cross-section of supply pipe 30. Because supply pipe 30 isa round pipe in the present exemplary embodiment, edge portion 23 is aring shape. Edge portion 23 and restraining plates 22 a and 22 b areformed monolithically.

Restraining plates 22 a and 22 b are arranged in linear symmetry withrespect to central axis 27 that passes through the center of the coverplate. In the cross-section of supply pipe 30, opening 21 is formed inareas other than edge portion 23 and restraining plates 22 a and 22 b.The shape of opening 21 also has linear symmetry with respect to centralaxis 27.

Opening 21 is of a configuration in which the length along the walls ofsupply pipe 30 and edge portion 23 (for example, arrows T1 and T2 ofboth directions shown in FIG. 3) continuously decreases in size from theperiphery to the center of the cross-section of supply pipe 30. Arrow T1indicates an example of the length of the side close to edge portion 23and arrow T2 indicates an example of the length of the side close to thecenter of the cover plate.

Focusing on the area of opening 21, opening 21 is shaped such that twofan-shaped openings are connected by way of a narrowed open portionparallel to central axis 27.

In the configuration shown in FIG. 3, the area of opening 21 in thevicinity of the center in the cross-section of supply pipe 30 to diehead 10 is small while the area of opening 21 in the vicinity of theperiphery is large. As a result, the flow rate of coating slurry isreduced in the vicinity of the center, and the flow rate of coatingslurry in the vicinity of the center is equivalent to the flow rate ofthe coating slurry of the periphery.

FIG. 4 is a transparent view when the die head shown in FIG. 2 is viewedfrom above.

FIG. 4 is for a case in which opening 14 shown in FIG. 2 is arrangedclose to the center with respect to the width direction of manifold 12.As shown in FIG. 4, cover plate 20 is arranged inside supply pipe 30such that central axis 27 shown in FIG. 3 is parallel to the widthdirection of manifold 12 and slit 11.

Regarding the method of arranging cover plate 20 with respect to diehead 12 in the following explanation, an arrangement such as shown inFIG. 4 is referred to as “horizontal placement” and an arrangement inwhich cover plate 20 shown in FIG. 4 is rotated 90 degrees is referredto as “vertical placement.” In other words, in the case of verticalplacement, central axis 27 of cover plate 20 is perpendicular to thewidth direction shown in FIG. 4.

Examples of modifications of the cover plate shown in FIG. 3 are nextdescribed.

(Modification 1)

FIGS. 5A and 5B are a top view and side view of Modification 1 of thecover plate. In the interest of convenience of explanation, the X-axis,Y-axis, and Z-axis are defined as shown in the figure.

In the cover plate of Modification 1, compared to the cover plate 20shown in FIG. 3, restraining plates 22 a and 22 b have tilted portions26 a and 26 b that are tilted toward the die-head 10 side from thecross-section of supply pipe 30 shown in FIG. 2.

As shown in FIG. 5B, tilted portions 26 a and 26 b are tilted in thedirection of the Z-axis (in the inflow direction of coating slurry 50).Angle θ1 indicated in FIG. 5B is 20°, and angle θ2 is 160°. Angles θ1and θ2 are merely examples.

In the configuration of Modification 1, although restraining plates 22 aand 22 b reduce the flow rate of coating slurry 50 in the vicinity ofthe center of the cross-section of supply pipe 30, tilted portions 26 aand 26 b have the effect of easing a reduction in the flow rate. As aresult, the effect can be expected that differences in the flow rate ofcoating slurry 50 in the cross-section of supply pipe 30 will graduallydecrease from the center to the periphery.

The results of appraisal of the coating active material layer realizedby the coating device of the present exemplary embodiment are nextdescribed.

The results of comparing the measurement results shown in FIG. 10 andthe next cases (1) and (2) are next described. Because the method ofappraising the coating active material layer is the same as the methoddescribed with reference to FIG. 10, detailed explanation is omitted.Case (1) is a case of using the cover plate described in FIG. 3(vertical placement and horizontal placement), and case (2) is a case inwhich the cover plate of Modification 1 is placed horizontally.

(1) When Using the Cover Plate Shown in FIG. 3:

When the cover plate shown in FIG. 3 was set in horizontal and verticalplacement, the variation was 0.43-0.59%, and the difference between themaximum value and minimum value of the coating weight of active materialper unit area was 1.6-1.9%. In the measurement results shown in FIG. 10,the variation was 0.70% and the difference between the maximum value andminimum value of the coating weight of active material per unit area was3% or more. It can thus be seen that, for the cover plate shown in FIG.3, the variation is lower than in the measurement results shown in FIG.10, and the difference between the maximum value and the minimum valueof the coating weight of active material per unit area is also lower.

(2) When the Cover Plate of Modification 1 is Set to HorizontalPlacement:

FIG. 6 is a graph showing the measurement results when the cover plateof Modification 1 is set in horizontal placement. The square blankpoints and the solid line that joins these points are the measuredpoints when the cover plate of Modification 1 is set in horizontalplacement. For the sake of comparison, FIG. 6 shows the graph shown inFIG. 10 overlaying the graph that shows the measurement results ofModification 1. The black square points and the broken line that joinsthese points correspond to the graph shown in FIG. 10.

Focusing on the variation, the variation is reduced to 0.12% inModification 1, in contrast to 0.70% in the graph shown in FIG. 10.Focusing on the difference between the maximum value and minimum valueof the coating weight of active material per unit area, the differenceis reduced to 0.5% in Modification 1, in contrast to 3% or more in thegraph shown in FIG. 10.

In the case of horizontal placement of the cover plate shown in FIGS. 5Aand 5B, central axis 27 shown in FIG. 5A is parallel to the widthdirection of die head 10, and as a result, the two fan-shaped openingsshown in FIG. 5A are arranged parallel to the width direction of diehead 10 on opposite sides of a narrowly constricted opening. It istherefore believed that the coating slurry in the vicinity of theperiphery that has a slower flow rate than in the vicinity of the centerin the supply pipe tends to disperse smoothly in the width direction ofeach of manifold 12 and slit 11. This effect is also similar for thecover plate shown in FIG. 3.

It is further believed that tilted portions 26 a and 26 b result in theaction of easing the force exerted by restraining plates 22 a and 22 bto reduce the flow rate of coating slurry 50 in the vicinity of thecenter of the cross-section of supply pipe 30.

Modifications of cover plate 20 are next described. FIGS. 7A to 7C aretop views showing the configurations of Modifications 2-4 of the coverplate. For the sake of expediency of explanation, the X-axis and Y-axisare defined similarly to FIG. 3.

(Modification 2)

The cover plate shown in FIG. 7A is of a configuration in which,compared to the cover plate shown in FIG. 3, a plurality of openings 51are formed in each of restraining plates 22 a and 22 b. In theconfiguration shown in FIG. 7A, five openings 51 are formed in each ofrestraining plate 22 a and restraining plate 22 b. Focusing on the sideof restraining plate 22 a, five openings 51 are arranged along the outerperiphery of the cover plate at the joining portion of restraining plate22 a which join with edge 23. The five openings 51 formed in restrainingplate 22 a and five openings 51 formed on restraining plate 22 b arearranged in linear symmetry with respect to central axis 27.

In the configuration of Modification 2, a plurality of openings 51 areprovided at the joining portions of restraining plates 22 a and 22 bwhich join with edge portions 23.

As a result, reduction in the flow rate of coating slurry 50 at theperiphery of the cross-section of supply pipe 30 shown in FIG. 2 can beeased.

In the present modification, restraining plates 22 a and 22 b may alsohave tilted portions 26 a and 26 b as shown in FIGS. 5A and 5B.

(Modification 3)

The cover plates shown in FIG. 7B is of a configuration in which,compared to the cover plates shown in FIG. 7A, openings 52 a and 52 bthat have an opening area greater than that of openings 51 are formed inrestraining plates 22 a and 22 b, respectively. Opening 52 a and opening52 b are arranged in linear symmetry with respect to central axis 27.

In the configuration of Modification 3, openings 52 a and 52 b thatextend in a direction from edge portion 23 toward the center areprovided in restraining plates 22 a and 22 b. As a result, the effectscan be expected include not only easing a reduction in the flow rate ofcoating slurry 50 at the periphery in the cross-section of supply pipe30 shown in FIG. 2, but also reducing the difference in the flow rate ofcoating slurry 50 from the center to the periphery in the cross-sectionof supply pipe 30.

In this modification as well, restraining plates 22 a and 22 b may alsohave tilted portions 26 a and 26 b, as shown in FIGS. 5A and 5B.

In the cases of the cover plates of Modification 2 and Modification 3,it is believed that, even when the cover plate is set to verticalplacement, the effect obtained can approach that of the case of settingthe cover plate in the horizontal placement.

(Modification 4)

The cover plate shown in FIG. 7C includes: frame-shaped edge portion 23along the walls of supply pipe 30 shown in FIG. 2, restraining plate 55that reduces the flow rate of coating slurry 50 in the center of thecross-section of supply pipe 30, and openings 53 a-53 d formed alongedge portion 23 at the periphery of restraining plate 55. Opening 53 aand opening 53 c are arranged in linear symmetry with respect to theaxis that passes through the center of the cover plate and that isparallel to the X-axis. In addition, opening 53 b and opening 53 d arearranged in linear symmetry with respect to the axis that passes throughthe center of the cover plate and that is parallel to the Y-axis.

In the configuration of Modification 4, opening 53 a and opening 53 care arranged in linear symmetry with respect to the axis that passesthrough the center of the cover plate, and opening 53 b and opening 53 dare arranged in linear symmetry with respect to another axis that isorthogonal to the aforementioned axis. The effect is therefore obtainedthat regardless of whether the cover plate is set to vertical orhorizontal placement, the flow rate of the coating slurry in thecross-section of the supply pipe is equalized. Although a case is shownin FIG. 7C in which there are four openings 53 a-53 d, the number ofopenings is not limited to four.

In the coating device of the present exemplary embodiment, a cover platethat is provided in the supply port or supply pipe of the coating slurryto the die head has a construction by which the force that reduces theflow rate in the center is greater than the force that reduces the flowrate at the periphery in the cross-section of the supply port or thesupply pipe. As a result, the flow rate of the coating slurry is reducedin the center of the cross-section of the supply port or the supplypipe, and the coating slurry is uniformly dispensed with respect to thewidth direction of the slit, from the slit by way of the manifold. As aresult, the thickness of the coating active material layer that isapplied to a current collector is uniform with respect to the widthdirection of the current collector, and the uniformity of the coatingweight of active material per unit area of the coating active materiallayer is improved.

In addition, in the method disclosed in Patent Document 1, the die headmust be disassembled and then a flow amount adjustment plate isinstalled, but in the present exemplary embodiment, the cover plate ofthe present exemplary embodiment need only be installed in the supplyport or supply pipe for supplying coating slurry to the die head. As aresult, the uniformity of the coating layer thickness can be improved bya method that is more convenient than the method disclosed in PatentDocument 1.

While the invention has been particularly shown and described withreference to exemplary embodiments thereof, the invention is not limitedto these exemplary embodiments. It will be understood by those ofordinary skill in the art that various changes in form and details maybe made therein without departing from the spirit and scope of thepresent invention as defined by the claims.

This application is based upon and claims the benefit of priority fromJapanese Patent Application No. 2015-185492, filed on Sep. 18, 2015, thedisclosure of which is incorporated herein in its entirety by reference.

EXPLANATION OF REFERENCE NUMBERS

-   10 die head-   11 slit-   12 manifold-   13 supply port-   20 cover plate-   30 supply pipe-   50 coating slurry

What is claimed is:
 1. A coating method that uses a coating devicecomprising at least: a die head including a supply port into which acoating slurry is supplied, a manifold that stores the coating slurry,and a slit that dispenses the coating slurry that is stored in themanifold; and a supply pipe having one end connected to the supply port;said method comprising steps of: reducing a flow rate of the coatingslurry greater in a center than at a periphery of a cross-section thatis orthogonal to a direction in which the coating slurry into the supplypipe; and supplying the coating slurry to the supply port.
 2. Thecoating method as set forth in claim 1, wherein the flow rate of thecoating slurry greater in the center than at the periphery of across-section that is orthogonal to the direction in which the coatingslurry into the supply pipe is reduced, the flow rate of the coatingslurry in a vicinity of a wall surface of the supply pipe is maintained,and the coating slurry is supplied to the supply port.